A strand can be, for example, a cable having a conductor and insulation surrounding the conductor. There is a need to measure such strands, in particular to determine the position or the diameter. An optical measurement of strand-shaped goods is known from EP 0 924 493 B1, for example, in which using coherent monochromatic light, preferably from a laser diode, a shadow of the strand to be measured is projected without imaging optics onto a light sensor. Compared to measurement methods that function using imaging optics, highly accurate measurements can be attained using this method with comparably small dimensions of the arrangement. Diffraction borders are generated on the geometric shadow boundaries of the strand due to the coherent monochromatic radiation of the light source. These geometric shadow boundaries can be determined from the recorded diffraction borders. This is possible, for example, by comparing to a reference diffraction pattern known from diffraction theory. The free parameters of this reference pattern, in particular the extension and the local shift, are varied until an optimal correlation arises between the reference diffraction pattern and the profile of the measured diffraction border intensity. This correlation is, however, computationally relatively intensive. Alternatively, the position of characteristic feature points of the diffraction border, for example local intensity maximums and minimums, are evaluated, and the position of the geometric shadow boundary can be concluded therefrom.